The Elasticsearch SAML implementation makes use of the Elasticsearch Token Service. This service
is automatically enabled if you configure TLS on the HTTP interface, and can be
explicitly configured by including the following in your elasticsearch.yml file:

SAML authentication is enabled by configuring a SAML realm within the
authentication chain for Elasticsearch.

This realm has a few mandatory settings, and a number of optional settings.
The available settings are described in detail in the
SAML realm documentation, this guide will walk you through
the most common settings.

Create a realm by adding the following to your elasticsearch.yml
configuration file. Each configuration value is explained below.

SAML is used when authenticating via Kibana, but it is not an
effective means of authenticating directly to the Elasticsearch REST API. For this reason
we recommend that you include at least one additional realm such as the
native realm in your authentication chain for use by API
clients.

The configuration values used in the example above are:

xpack.security.authc.realms.saml.saml1

This defines a new saml authentication realm named "saml1".
See Realms for more explanation of realms.

order

You should define a unique order on each realm in your authentication chain.
It is recommended that the SAML realm be at the bottom of your authentication
chain (that is, that it has the highest order).

idp.metadata.path

This is the path to the metadata file that you saved for your Identity Provider.
The path that you enter here is relative to your config/ directory.
Elasticsearch will automatically monitor this file for changes and will
reload the configuration whenever it is updated.

idp.entity_id

This is the identifier (SAML EntityID) that your IdP uses.
It should match the entityID attribute within the metadata file.

sp.entity_id

This is a unique identifier for your Kibana instance, expressed as a URI.
You will use this value when you add Kibana as a service provider within your IdP.
We recommend that you use the base URL for your Kibana instance as the entity ID.

sp.acs

The Assertion Consumer Service (ACS) endpoint is the URL within Kibana that accepts
authentication messages from the IdP.
This ACS endpoint supports the SAML HTTP-POST binding only.
It must be a URL that is accessible from the web browser of the user who is
attempting to login to Kibana, it does not need to be directly accessible by Elasticsearch
or the IdP.
The correct value may vary depending on how you have installed Kibana and
whether there are any proxies involved, but it will typically be
${kibana-url}/api/security/v1/saml where ${kibana-url} is the base URL for
your Kibana instance.

sp.logout

This is the URL within Kibana that accepts logout messages from the IdP.
Like the sp.acs URL, it must be accessible from the web browser, but does
not need to be directly accessible by Elasticsearch or the IdP. The correct value may
vary depending on how you have installed Kibana and whether there are any
proxies involved, but it will typically be ${kibana-url}/logout where
${kibana-url} is the base URL for your Kibana instance.

When a user connects to Kibana through your Identity Provider, the Identity
Provider will supply a SAML Assertion about the user. The assertion will contain
an Authentication Statement indicating that the user has successfully
authenticated to the IdP and one or more Attribute Statements that will
include Attributes for the user.

These attributes may include such things as:

the user’s username

the user’s email address

the user’s groups or roles

Attributes in SAML are named using a URI such as
urn:oid:0.9.2342.19200300.100.1.1 or
http://schemas.xmlsoap.org/ws/2005/05/identity/claims/upn, and have one or
more values associated with them.

These attribute identifiers vary between IdPs, and most IdPs offer ways to
customize the URIs and their associated value.

Elasticsearch uses these attributes to infer information about the user who has
logged in, and they can be used for role mapping (below).

In order for these attributes to be useful, Elasticsearch and the IdP need to have a
common value for the names of the attributes. This is done manually, by
configuring the IdP and the SAML realm to use the same URI name for
each logical user attribute.

The recommended steps for configuring these SAML attributes are as follows:

Consult your IdP to see what user attributes it can provide.
This varies greatly between providers, but you should be able to obtain a list
from the documentation, or from your local admin.

Read through the list of user properties that Elasticsearch
supports, and decide which of them are useful to you, and can be provided by
your IdP. At a minimum, the principal attribute is required.

Configure your IdP to "release" those attributes to your Kibana SAML service
provider. This process varies by provider - some will provide a user interface
for this, while others may require that you edit configuration files.
Usually the IdP (or your local administrator) will have suggestions about what
URI to use for each attribute. You can simply accept those suggestions, as the
Elasticsearch service is entirely configurable and does not require that any specific
URIs are used.

Configure the SAML realm in Elasticsearch to associate the Elasticsearch user properties (see
the listing below), to the URIs that you configured
in your IdP. In the example above, we have configured the principal and
groups attributes.

In general, Elasticsearch expects that the configured value for an attribute will be a
URI such as urn:oid:0.9.2342.19200300.100.1.1, however there are some
additional names that can be used:

nameid

This uses the SAML NamedID value instead of a SAML attribute. SAML
NameID elements are an optional, but frequently provided, field within a
SAML Assertion that the IdP may use to identify the Subject of that
Assertion. In some cases the NameID will relate to the user’s login
identifier (username) within the IdP, but in many cases they will be
internally generated identifiers that have no obvious meaning outside
of the IdP.

nameid:persistent

This uses the SAML NameID value, but only if the NameID format is
urn:oasis:names:tc:SAML:2.0:nameid-format:persistent.
A SAML NameID element has an optional Format attribute that indicates
the semantics of the provided name. It is common for IdPs to be configured
with "transient" NameIDs that present a new identifier for each session.
Since it is rarely useful to use a transient NameID as part of an attribute
mapping, the "nameid:persistent" attribute name can be used as a safety
mechanism that will cause an error if you attempt to map from a NameID
that does not have a persistent value.

Identity Providers can be either statically configured to release a NameID
with a specific format, or they can be configured to try to conform with the
requirements of the SP. The SP declares its requirements as part of the
Authentication Request, using an element which is called the NameIDPolicy. If
this is needed, you can set the relevant settings named
nameid_format in order to request that the IdP releases a NameID with a
specific format.

friendlyName

A SAML attribute may have a friendlyName in addition to its URI based name.
For example the attribute with a name of urn:oid:0.9.2342.19200300.100.1.1
might also have a friendlyName of uid.
You may use these friendly names within an attribute mapping, but it is
recommended that you use the URI based names, as friendlyNames are neither
standardized or mandatory.

The example below configures a realm to use a persistent nameid for the principal,
and the attribute with the friendlyName "roles" for the user’s groups.

The Elasticsearch SAML realm can be configured to map SAML attributes to the
following properties on the authenticated user:

principal

(Required)
This is the username that will be applied to a user that authenticates
against this realm.
The principal appears in places such as the Elasticsearch audit logs.

groups

(Recommended)
If you wish to use your IdP’s concept of groups or roles as the basis for a
user’s Elasticsearch privileges, you should map them with this attribute.
The groups are passed directly to your
role mapping rules

There are some occasions where the IdP’s attribute may contain more information
than you wish to use within Elasticsearch. A common example of this is one where the
IdP works exclusively with email addresses, but you would like the user’s
principal to use the local-name part of the email address.
For example if their email address was james.wong@staff.example.com, then you
would like their principal to simply be james.wong.

This can be achieved using the attribute_patterns setting in the Elasticsearch
realm, as demonstrated in the realm configuration below:

In this case, the user’s principal is mapped from an email attribute, but a
regular expression is applied to the value before it is assigned to the user.
If the regular expression matches, then the result of the first group is used as
effective value. If the regular expression does not match then the attribute
mapping fails.

In this example, the email address must belong to the staff.example.com domain,
and then the local-part (anything before the @) is used as the principal.
Any users who try to login using a different email domain will fail because the
regular expression will not match against their email address, and thus their
principal attribute - which is mandatory - will not be populated.

Small mistakes in these regular expressions can have significant
security consequences. For example, if we accidentally left off the trailing
$ from the example above, then we would match any email address where the
domain starts with staff.example.com, and this would accept an email
address such as admin@staff.example.com.attacker.net. It is important that
you make sure your regular expressions are as precise as possible so that
you do not inadvertently open an avenue for user impersonation attacks.

It is sometimes necessary for a SAML SP to be able to impose specific
restrictions regarding the authentication that will take place at an IdP,
in order to assess the level of confidence that it can place in
the corresponding authentication response. The restrictions might have to do
with the authentication method (password, client certificates, etc), the
user identification method during registration, and other details. Elasticsearch implements
SAML 2.0 Authentication Context, which can be used for this purpose as defined in SAML 2.0 Core
Specification.

In short, the SAML SP defines a set of Authentication Context Class Reference
values, which describe the restrictions to be imposed on the IdP, and sends these
in the Authentication Request. The IdP attempts to grant these restrictions.
If it cannot grant them, the authentication attempt fails. If the user is
successfully authenticated, the Authentication Statement of the SAML Response
contains an indication of the restrictions that were satisfied.

You can define the Authentication Context Class Reference values by using the req_authn_context_class_ref option in the SAML realm configuration. See
SAML realm settings.

Elasticsearch supports only the exact comparison method for the Authentication Context.
When it receives the Authentication Response from the IdP, Elasticsearch examines the
value of the Authentication Context Class Reference that is part of the
Authentication Statement of the SAML Assertion. If it matches one of the
requested values, the authentication is considered successful. Otherwise, the
authentication attempt fails.

The SAML protocol supports the concept of Single Logout (SLO).
The level of support for SLO varies between Identity Providers.
You should consult the documentation for your IdP to determine what Logout
services it offers.

By default the Elastic Stack will support SAML SLO if the following are true:

One of the values that Elasticsearch reads from the IdP’s SAML metadata is the
<SingleLogoutService>. In order for Single Logout to work with the Elastic
stack, Elasticsearch requires that this exist and support a binding of
urn:oasis:names:tc:SAML:2.0:bindings:HTTP-Redirect.

The Elastic Stack will send both <LogoutRequest> and <LogoutResponse>
messages to this service as appropriate.

If your IdP provides a <SingleLogoutService> but you do not wish to use it,
you can configure idp.use_single_logout: false in your SAML realm, and Elasticsearch
will ignore the SLO service that your IdP provides. In this case, when a user
logs out of Kibana it will invalidate their Elasticsearch session (security token), but
will not perform any logout at the IdP.

If your IdP does not support Single Logout, or you choose not to use it, then
Kibana will perform a "local logout" only.

This means that Kibana will invalidate the session token it is using to
communicate with Elasticsearch, but will not be able to perform any sort of invalidation
of the Identity Provider session. In most cases this will mean that Kibana users
are still considered to be logged in to the IdP. Consequently, if the user
navigates to the Kibana landing page, they will be automatically reauthenticated,
and will commence a new Kibana session without needing to enter any credentials.

The possible solutions to this problem are:

Ask your IdP administrator or vendor to provide a Single Logout service

If your Idp does provide a Single Logout Service, make sure it is included in
the IdP metadata file, and do not set idp.use_single_logout to false.

Advise your users to close their browser after logging out of Kibana

Enable the force_authn setting on your SAML realm. This setting causes the
Elastic Stack to request fresh authentication from the IdP every time a user
attempts to log into Kibana.
This setting defaults to false because it can be a more cumbersome user
experience, but it can also be an effective protection to stop users
piggy-backing on existing IdP sessions.

The Elastic Stack supports generating signed SAML messages (for authentication
and/or logout), verifying signed SAML messages from the IdP (for both
authentication and logout) and can process encrypted content.

You can configure Elasticsearch for signing, encryption or both, with the same
or separate keys used for each of those.

The Elastic Stack uses X.509 certificates with RSA private keys for SAML
cryptography. These keys can be generated using any standard SSL tool, including
the elasticsearch-certutil tool.

Your IdP may require that the Elastic Stack have a cryptographic key for signing
SAML messages, and that you provide the corresponding signing certificate within
the Service Provider configuration (either within the Elastic Stack SAML
metadata file or manually configured within the IdP administration interface).
While most IdPs do not expected authentication requests to be signed, it is
commonly the case that signatures are required for logout requests. Your IdP
will validate these signatures against the signing certificate that has been
configured for the Elastic Stack Service Provider.

Encryption certificates are rarely needed, but the Elastic Stack supports them
for cases where IdPs or local policies mandate their use.

Elasticsearch supports certificates and keys in either PEM, PKCS#12 or JKS format.
Some Identity Providers are more restrictive in the formats they support, and
will require you to provide the certificates as a file in a particular format.
You should consult the documentation for your IdP to determine what formats they
support. Since PEM format is the most commonly supported format, the examples
below will generate certificates in that format.

The Elasticsearch security features support a single key for message decryption. If a
key is configured, then Elasticsearch attempts to use it to decrypt
EncryptedAssertion and EncryptedAttribute elements in Authentication
responses, and EncryptedID elements in Logout requests.

Elasticsearch rejects any SAML message that contains an EncryptedAssertion
that cannot be decrypted.

If an Assertion contains both encrypted and plain-text attributes, then
failure to decrypt the encrypted attributes will not cause an automatic
rejection. Rather, Elasticsearch processes the available plain-text attributes
(and any EncryptedAttributes that could be decrypted).

If you wish to use PEM formatted keys and certificates for SAML encryption,
then you should configure the following settings on the SAML realm:

encryption.certificate

The path to the PEM formatted certificate file. e.g. saml/saml-crypt.crt

encryption.key

The path to the PEM formatted key file. e.g. saml/saml-crypt.key

encryption.secure_key_passphrase

The passphrase for the key, if the file is encrypted. This is a
secure setting that must be set with the
elasticsearch-keystore tool.

If you wish to use PKCS#12 formatted files or a Java Keystore for SAML
encryption, then you should configure the following settings on the SAML realm:

encryption.keystore.path

The path to the PKCS#12 or JKS keystore. e.g. saml/saml-crypt.p12

encryption.keystore.alias

The alias of the key within the keystore. e.g. encryption-key

encryption.keystore.secure_password

The passphrase for the keystore, if the file is encrypted. This is a
secure setting that must be set with the
elasticsearch-keystore tool.